摘要
堡若勒斯湖(Borullus)位于尼罗河三角洲正中央。大约公元8世纪时,由于河流沉积,在湖的北面形成了许多沙丘,继而,在这道屏障后面,先前存在的潮汐湿地沉降形成了一个盐沼,堡若勒斯湖可能就是从这个盐沼演化而来。每年9～12月,尼罗河的支流赛本尼提克(Sebennytic)定期泛滥,洪水从一个出口布法兹(Bughaz)排出。在河流低水位时,这个过程逆转过来,布法兹成为海水的入口。由于这个转换过程,它的动植物群落混合了了海水、淡水和咸水物种。大约19世纪中期已经开始在尼罗河上修建水坝,最终以1964年阿斯旺大坝的建成结束,这使得每年的洪水完全得到控制。因此,一个流量稳定的、可保证三角洲农业灌溉的尼罗河开始注入湖泊,并且形成固定的通往地中海的出海口;湖水几乎全部变为淡水,先前以胭脂鱼为基础的海产渔业转化成了以棘鳍类热带淡水鱼-鲶鱼为基础的淡水渔业。但是,在水稻和三角洲其它新的农作物种植过程中产生大量的营养物质排入。目前,湖泊已经富营养化,仅仅依赖其很短的滞留期来抵制超营养化。最终,尼罗河大坝终止了每年沉积物向三角洲的流入,但是沉陷和海岸侵蚀仍然继续,并且正在吞噬将湖泊与海洋分隔开来的沙坝。
Borullus,the most centrally situated of the Nile Delta lakes,probably evolved around the eighth century AD from a preexisting salt marsh by fluviatile deposition of sand dunes north of the lake and subsidence of the preexisting tidal swamp behind this barrier.It was flooded yearly (September-December) by the Sebennytic branch of the Nile,and evacuated water through an exit, Bughaz.At low river levels,this process reversed and Bughaz functioned as a marine inlet.Because of this switch,its fauna and flora contained a mix of marine,freshwater,and brackish-water species.Around the mid-nineteenth century,damming of the Nile began,culminating with the high Aswan Dam (1964) that brought the yearly flood fully under control.As a result,a steady flow of Nile water,used for irrigated delta agriculture,began to drain to the lake and became a constant evacuator to the Mediterranean.It turned almost fresh,and its fishery,formerly marine and mullet-based,became cichlid-catfish based.However,rice and other new delta crops caused huge amounts of nutrients to wash down the drains,and currently the lake is eutrophied and only resists hypertrophication because of the low residence time of its water.Finally,the damming of the Nile terminated the influx to the delta of a yearly sediment layer,but subsidence and coastal erosion continue and are now consuming the sand bar that separates the lake from the sea.
